#-*- coding:UTF-8 -*-
#原來建立物件時或者是呼叫類以外的方法時提示沒有定義是因為這些類或方法的位置不應該放在主函式後面，而應該放在主函式前面
import urlparse
import urllib2
import random
import time
from datetime import datetime, timedelta
import socket
import robotparser
import csv
import re
import lxml.html
DEFAULT_AGENT = 'wswp'
DEFAULT_DELAY = 5
DEFAULT_RETRIES = 1
 
DEFAULT_TIMEOUT = 60
def link_crawler(seed_url, link_regex=None, max_depth=-1, max_urls=-1, user_agent='wswp',  scrape_callback=None, cache=None):
    """Crawl from the given seed URL following links matched by link_regex
    """
    # the queue of URL's that still need to be crawled 雙向佇列裡面儲存url
crawl_queue = [seed_url]
    # the URL's that have been seen and at what depth
 
seen = {seed_url: 0}
    # track how many URL's have been downloaded
num_urls = 0
rp = get_robots(seed_url)#獲取robots.txt
D = Downloader(DEFAULT_DELAY, DEFAULT_AGENT, None, DEFAULT_RETRIES, DEFAULT_TIMEOUT, None, None)
    while crawl_queue:
        url = crawl_queue.pop()#移除列表中的元素，並且返回該元素的值
depth = seen[url]
        # check url passes robots.txt restrictions
 
if rp.can_fetch(user_agent, url):#確定指定的使用者代理是否允許訪問網頁
html = D(url)
            links = []
            if scrape_callback:
                links.extend(scrape_callback(url, html) or [])
            depth = seen[url]
            if depth != max_depth:
                # can still crawl further
if link_regex:
                    # filter for links matching our regular expression
links.extend(link for link in get_links(html) if re.match(link_regex, link))

                for link in links:
                    link = normalize(seed_url, link) #返回絕對連結
# check whether already crawled this link
if link not in seen:
                        seen[link] = depth + 1
# check link is within same domain
if same_domain(seed_url, link):
                            # success! add this new link to queue
crawl_queue.append(link)

            # check whether have reached downloaded maximum
num_urls += 1
if num_urls == max_urls:
                break
        else:
            print 'Blocked by robots.txt:', url

def get_robots(url):
    """Initialize robots parser for this domain
    """
rp = robotparser.RobotFileParser()
    rp.set_url(urlparse.urljoin(url, '/robots.txt'))#絕對連結
rp.read()
    return rp

def normalize(seed_url, link):
    """Normalize this URL by removing hash and adding domain
    """
link, _ = urlparse.urldefrag(link)  # remove hash to avoid duplicates urldefrag(url)將url分解成去掉fragment的新url和去掉的fragment的二元組
return urlparse.urljoin(seed_url, link)#絕對連結
def same_domain(url1, url2):
    """Return True if both URL's belong to same domain
    """
    #將url分解成部件的6元組
return urlparse.urlparse(url1).netloc == urlparse.urlparse(url2).netloc

def get_links(html):
    """Return a list of links from html
    """
    # a regular expression to extract all links from the webpage
    #re.compile()函式將正則表示式的字串形式編譯為Pattern例項，然後使用Pattern例項處理文字並獲得匹配結果（一個Match例項），最後使用Match例項獲得資訊，進行其他的操作。
webpage_regex = re.compile('<a[^>]+href=["\'](.*?)["\']', re.IGNORECASE)
    # list of all links from the webpage
return webpage_regex.findall(html)

class Downloader:
    def __init__(self, delay=DEFAULT_DELAY, user_agent=DEFAULT_AGENT, proxies=None, num_retries=DEFAULT_RETRIES,
                 timeout=DEFAULT_TIMEOUT, opener=None, cache=None):
        socket.setdefaulttimeout(timeout)
        self.throttle = Throttle(delay)
        self.user_agent = user_agent
        self.proxies = proxies
        self.num_retries = num_retries
        self.opener = opener
        self.cache = cache

    def __call__(self, url):
        result = None
if self.cache:
            try:
                result = self.cache[url]
            except KeyError:
                # url is not available in cache
pass
            else:
                if self.num_retries > 0 and 500 <= result['code'] < 600:
                    # server error so ignore result from cache and re-download
result = None
if result is None:
            # result was not loaded from cache so still need to download
self.throttle.wait(url)
            proxy = random.choice(self.proxies) if self.proxies else None
headers = {'User-agent': self.user_agent}
            result = self.download(url, headers, proxy=proxy, num_retries=self.num_retries)
            if self.cache:
                # save result to cache
self.cache[url] = result
        return result['html']

    def download(self, url, headers, proxy, num_retries, data=None):
        print 'Downloading:', url
        request = urllib2.Request(url, data, headers or {})
        opener = self.opener or urllib2.build_opener()
        if proxy:
            proxy_params = {urlparse.urlparse(url).scheme: proxy}
            opener.add_handler(urllib2.ProxyHandler(proxy_params))
        try:
            response = opener.open(request)
            html = response.read()
            code = response.code
        except Exception as e:
            print 'Download error:', str(e)
            html = ''
if hasattr(e, 'code'):
                code = e.code
                if num_retries > 0 and 500 <= code < 600:
                    # retry 5XX HTTP errors
return self._get(url, headers, proxy, num_retries - 1, data)
            else:
                code = None
return {'html': html, 'code': code}


class ScrapeCallback:
    def __init__(self):
        self.writer = csv.writer(open('countries.csv', 'w'))
        self.fields = ('area', 'population', 'iso', 'country', 'capital',
          'continent', 'tld', 'currency_code', 'currency_name',
          'phone', 'postal_code_format', 'postal_code_regex', 'languages')
        self.writer.writerow(self.fields)

    def __call__(self, url, html):
        if re.search('view', url):
            tree = lxml.html.fromstring(html)
            row = []
            for field in self.fields:
                row.append(tree.cssselect('table > tr#places_{}__row > td.w2p_fw'.format(field))[0].text_content())
                self.writer.writerow(row)

class Throttle:
    """Throttle downloading by sleeping between requests to same domain
    """
def __init__(self, delay):
        # amount of delay between downloads for each domain
self.delay = delay
        # timestamp of when a domain was last accessed
self.domains = {}

    def wait(self, url):
        """Delay if have accessed this domain recently
        """
domain = urlparse.urlsplit(url).netloc
        last_accessed = self.domains.get(domain)
        if self.delay > 0 and last_accessed is not None:
            sleep_secs = self.delay - (datetime.now() - last_accessed).seconds
            if sleep_secs > 0:
                time.sleep(sleep_secs)
        self.domains[domain] = datetime.now()


if __name__ == '__main__':
    link_crawler('http://example.webscraping.com', '/(index|view)', scrape_callback=ScrapeCallback())